Hitherto, so-called rotary type fluid machines have been known in the art. Rotary type fluid machines are now widely used as compressors for refrigerant compression in refrigeration apparatus. On the other hand, JP, 2000-234814, A, patent gazette discloses a refrigeration apparatus. In this refrigeration apparatus, an expander serving as an expansion mechanism is provided in a refrigerant circuit and power is recovered from refrigerant which is a supercritical-state, high-pressure fluid. The above-described rotary type fluid machine may be used as an expander for power recovery. In this case, high-pressure fluid is introduced into the rotary type fluid machine servings as an expander and power is obtained by expansion of the high-pressure fluid. Power recovered by the expander is utilized to drive a compressor.
The operation of a rotary type fluid machine as an expander (i.e. a rotary type expander) is described. In a typical rotary type expander, the volume of an expansion chamber varies with the rotation of a rotating shaft. From the point of time when the volume of the expansion chamber decreases to a minimum, introduction of high-pressure fluid into the expansion chamber commences. Such high-pressure fluid introduction into the expansion chamber is terminated at the point of time when the rotational angle of the rotating shaft reaches a predetermined value. And, thereafter, the refrigerant expands within the expansion chamber which is hermetically closed, whereby the rotating shaft is rotated by refrigerant expansion. In other words, within a single rotation of the rotating shaft in the rotary type expander, there are two different periods, during one of which there is high-pressure fluid flow into the expansion chamber and during the other of which there is no high-pressure fluid flow into the expansion chamber.